310 
FXUS65 KCYS 231650
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1050 AM MDT Fri Apr 23 2021

.SHORT TERM...(Today and tonight)
Issued at 325 AM MDT Fri Apr 23 2021

Overnight GOES WV/IR imagery showed shortwave troughs over the northeast
Great Plains and western MT to AZ. A surface cold front extended from
northeast ND through western SD, central WY and southern UT. Low/mid
level clouds prevailed behind the front, with pockets of light snow.
Temperatures were in the 20s to mid 30s. Winds were westerly 5-10 kt.

The cold front and shortwave trough will progress south and east across
the CWA today. Scattered low elevation rain showers and high elevation
snow showers will develop west of the Laramie Range this morning, and
east through southeast WY this afternoon. Colder air aloft will produce
modest lapse rates, with SBCAPEs upwards of 300 j/kg this afternoon.
There is the potential for isolated snow squalls over and near the
Snowy and Sierra Madre Ranges, as well as isolated thunderstorms along
and south of I-80. Storms that develop may generate wind gusts up to
40 kt. The showers will diminish from west to east tonight. Ahead of
the cold front, afternoon temperatures will rise into the 50s to around
60, with 40s behind the front. Lows tonight will cool into the 20s.

.LONG TERM...(Saturday through Thursday)
Issued at 325 AM MDT Fri Apr 23 2021

Upper ridge over the Intermountain West will translate east and flatten
over the Rockies and High Plains Saturday, resulting in a west-southwest
flow aloft. A upper low off the WA/OR coast will weaken to an open wave
as it moves inland Sunday. Flow aloft downstream of the trough will
increase from the southwest. 700mb temperatures will moderate to 2 to
4C by Sunday. Expect dry conditions with surface temperatures warming
into the 50s and 60s Saturday, and 60s to mid 70s Sunday. It will be
breezy both days, especially Sunday with gusts of 30 to 40 kt west of
the Laramie Range.

Enjoy this weekend's weather as a pattern change is forecast beginning
Monday with the approach of a deep upper trough and Pacific cold front.
Moisture will advance into the CWA, with scattered showers developing
west of the Laramie Range Monday morning and spreading to the I-25
corridor in the afternoon. It will remain warm ahead of the front over
the eastern plains with highs from 65 to 75, cooling into the 50s behind
the front. The GFS is the more progressive of the model solutions, with
the ECMWF and CMC slower. A blend of the models would keep cool and
showery weather in the forecast through Wednesday. Modest low/mid level
lapse rates may result in SBCAPEs near 200 j/kg Tuesday afternoon, which
may generate isolated thunderstorms. Following the departure of the
upper trough Thursday, northwest flow aloft will bring a return 
to drier conditions, with temperatures moderating to near seasonal
normals.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1039 AM MDT Fri Apr 23 2021

VFR conditions will continue for all TAF sites until 21Z. Isolated
thunderstorms will arrive to southeastern Wyoming TAF sites KLAR 
and KCYS starting 19Z which will bring visibility levels lower to
MVFR from 21Z to 0Z at KCYS. KRWL will continue in VFR conditions
but there is a possibility of VCSH impacting the TAF site. MVFR
conditions are possible for the western Nebraska Panhandle sites
due to the light rain showers arriving for KSNY, KAIA, KCDR, and 
KBFF starting 0Z until late Friday evening. There is a small
possibility of fog and afterwards light snow for KLAR at 08Z due 
to low level mositure but forecast confidence is low at this time.


&&

.FIRE WEATHER...
Issued at 300 AM MDT Fri Apr 23 2021

A cold front and upper level disturbance will move through the region
today, accompanied by scattered rain showers, snow showers, and isolated
weak thunderstorms. The showers will end from west to east this evening.
Warmer, drier and breezy conditions will develop this weekend. Gusty
winds, low humidities and prime fuels will increase the fire danger
from the far southeast Wyoming plains across the southern Nebraska
Panhandle Monday afternoon. Another cold front will move through the
districts Monday night. A showery and cool weather pattern will persist
into the middle of next week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...MAJ
LONG TERM...MAJ
AVIATION...AW
FIRE WEATHER...MAJ